There is known a monitoring system for reducing the risk of, in response to the fact that a user leaves a terminal, a third party operating the terminal. For example, the related techniques are disclosed in Japanese Laid-open Patent Publication No. 2014-6718. In an idle monitoring system, a server device assumes that when a user authorized through authentication to use a terminal leaves his seat and is temporarily away from the terminal, a state in which the server device is not accessed (idle state) will occur, and monitors the time over which the idle state is retained. Then, if this idle state time exceeds a certain time period, the server device invalidates the authorization and, when the user next uses the terminal, requests the user to re-authenticate. Thus, it is possible to reduce the risk of, after the user has left his seat, a third party impersonating a valid user and operating the terminal.